Rotary fan



March 8, 1955 c, HATHAWAY ET AL 2,703,625

ROTARY FAN Filed May 16, 1952 V IN VEN TORS 0 4,9555- ,4. M77664 WA YW/LU/IM E. CASH-EN ATTORNEY United States Patent ROTARY FAN Charles A.Hathaway, Litchfield, and William E. Cashen,

Torrington, Conn., assignors to The Torrington Manufacturing Company,Torrington, Conn., a corporation of Connecticut Application May 16,1952, Serial No. 288,160

3 Claims. (Cl. 170-159) This invention relates to a rotary fan adaptedfor a wide variety of uses.

It is the general object of the invention to provide an efficient rotaryfan which is characterized by its quiet pperation whether used as a freeair fan or as a pressure A more specific object of the invention is toprovide a fan which will lower the noise level, as compared toconventional fans, when applied to installations wherein the fan is tooperate at a constant preselected speed under constant airflowconditions.

An important aspect of the invention is the provision in each blade ofthe fan of forwardly, relatively sharply, curved leading and trailingportions which join the main portion in angularly related juncturelines. The curved leading portion includes part of the leading edge ofthe blade and a part of the peripheral edge of the blade. The saidleading portion is so curved as to reduce the angle of pitch of theleading edge adjacent the peripheral edge to approximately Zero. Thisfeature of construction provides the fan with advantages, as compared toconventional fans, for installations requiring a specific operatingspeed accompanied by a specific, constant flow of air and wherein amaximum sound level is prescribed. It is believed that the curvedleading portion minimizes the operating noise while the curved trailingportion increases the brake horsepower to maintain the desired operatingspeed under the prescribed constant condition of air flow.

Additional important objects and aspects of the invention will becomeapparent from the following description of the annexed drawing. It willbe understood that changes may be made from the construction shown, andthat the drawing and the specific description thereof are not to beconstrued as limiting the scope of the invention, the claims forming apart of the specification being relied upon for that purpose. It willalso be understood that all dimensions shown on the drawing and referredto in the specification are intended to clarify the explanation, andthat the invention is limited to particular angles and dimensions onlyto the extent set forth in the claims.

Of the drawing:

Fig. l is a front view of a rotary fan embodying the principles of thepresent invention;

Fig. 2 is a side elevational view of the fan shown in Fig. 1;

Fig. 3 is a front view of an unformed blank for one of the blades of thefan;

Fig. 4 is a sectional view taken along the line 44 of Fig. 3 but showinga blade formed from the blank; and

Figs. 5, 6 and 7 are enlarged views taken respectively along the lines5-5, 66 and 77 of Fig. 1 to show the true angles of pitch or bite at aplurality of radially spaced arcuate sections through a blade.

For purposes of exemplification, the fan shown in the drawing hascircumaxially spaced blades 10, 10, the spacings being shown as equal.Three blades are shown, but a larger or smaller number of blades may beprovided. The blades 10, 10 may be arranged for rotation in anyconventional manner. For example, the said blades can be formed from asingle sheet of stock which is provided with a central web forattachment to a shaft. In the example shown, each of the blades 10, 10is independently fabricated and is connected to a hub 12 secured as by aset screw 14 to a rotatable shaft 16. Preferably, the blades areindirectly connected to the hub by means of a spider 18 which may beconveniently fabricated from 8 2,703,625 Patented Mar. 8, 1955 sheetmetal so as to have a central portion 20 and integrally formed arms 22,22 corresponding in number to the blades 10, 10.

The central portion 20 of the spider is rigidly secured to the hub 12 ina plane perpendicular to the axis of rotation of the hub and shaft. Thespider arms 22, 22 thus extend radially outwardly to secure the bladesas by rivets 24, 24 or the like. The arms 22, 22 are deformed adjacentthe central portion 20 so that the extending portions of said arms willeach be pitched to the same angle about an axis lying in the plane ofthe central portion of the spider. Since the arms 22, 22 secure theblades 10, 10, the central portion 26 of each blade will be disposed atthe same pitch angle as the arms. The pitch angle of the arms 22, 22 mayvary throughout a wide range, as for example from 20 to 40, dependingupon the requirements of the particular installation. In the exemplaryfan shown, the spider arms and blades are set at a 33 angle of pitchwhich will be referred to hereinafter as the basic pitch angle. Thepitch angles of portions of each blade will differ from the pitch of thecentral portion 26 as a result of forming the blade in the manner whichwill now be described.

Each blade 10 is formed from a blank 28 as shown in Fig. 3, the blankbeing provided with holes 30, 30 for the rivets 24, 24. It should beunderstood that Fig. 3 is a front view of the blank 28 and that the lineA-B shown thereon, which extends approximately through the center of theblank, is the line about which the formed blade is rotated or pitched 33to the projected View shown in Fig. 1, each of the lines A-B extendingradially from the axis of rotation of the fan and lying in the plane ofthe central portion of the spider as mentioned above.

Since the fan is to be rotated in the clockwise direction as viewed inFig. 1, that half of the blank 28 on the right hand side of line A-B inFig. 3 will be referred to as the leading half and that half on the lefthand side of line AB will be referred to as the trailing half. The fanas shown has a diameter of 11 and the blank is dimensioned accordinglyto suit the blade formed therefrom to the particular fan shown.

' The blank may be conveniently fabricated from a sheet metal body so asto have an arcuate outer peripheral edge 32 and an arcuate inner edge34. The edge 32 of the blank is substantially bisected by the line ABand said edge of the blank is struck on a 7" radius so that theprojection of said edge when viewed as in Fig. 1 will be substantiallyconcentric to the hub when the formed blade is disposed at the pitchangle in the construction of the fan. The inner edge 34 of eachblade-forming blank is struck on a 1 radius from the axis of rotation.The fan, as shown, has a radius of 5 /2 and therefore the radius ofinner edge 34 is about 24% of said fan radius.

The leading half of the blank 28 is provided with an exposed leadingedge which includes an arcuate edge 36 connected with the peripheraledge 32 and the inner edge 34 at the more sharply curved arcuate edges38 and 40, respectively. In the exemplary blank shown the edge 36 isstruck on a 2 /2" radius which is equal to about 45% of the fan radius.It will be observed that the leading half of the blank is bounded byinterconnected arcuate edges of which the leading edge 36 and peripheraledge 32 are convexly curvilinear.

The trailing half of the blank 28 is provided with an exposed trailingedge which includes an arcuate edge 42 connected with the peripheraledge 32 and inner edge 34 at the more sharply curved arcuate edges 44and 46, respectively. In the exemplary blank shown, the edge 42 isstruck on a 2 radius which is equal to about 51% of the fan radius. Itwill be observed that the trailing half is bounded by arcuate edges ofwhich the trailing edge 42 and peripheral edge 32 are convexlycurvilinear.

When the aforedescribed blank 28 is shaped into a blade 10, a portion ofeach of the leading and trailing halves is formed intoparti-cylindroidal configuration so as to constitute a section of acylinder tangent to the flat central portion 26 of the blank. This isaccomplished in the leading half by curving the portion indicated by thereference numeral 50 sharply forwardly so that said portion will betangent to the central portion 26 along a juncture line AC. It will beapparent that the portion 50, in order to assume parti-cylindroidalconfiguration, will be curved along arcuate lines perpendicular to thejuncture line AC. A representative arcuate line is shown in Fig. 3 bythat portion of section line 44 to the right of juncture line AC. Thecurvature of the portion 50 along line 44 is shown in Fig. 4 and, aspointed out above, said forward curvature is relatively sharp. Theradius of forward curvature selected for the portion 50 depends upon thesize of the fan and the basic pitch angle of the blades, i. e., thepitch angle of the spider arms and of the central blade 26. For example,for the ll" diameter fan shown, with blades set at a basic pitch of 20to 40, the said radius of forward curvature should fall within the rangeof l to 2", which is to say that the radius of forward curvature shouldbe approximately 18% to approximately 36% of the radius of the fan. Whenthe blades are set a basic pitch of 33 as shown, the radius of forwardcurvature should closely approximate 1 /2". The radius of forwardcurvature will vary inversely with the basic pitch angle to effect adesired variation in the pitch angle along the leading edge of eachblade as Will be pointed out hereinafter.

That portion of the trailing half of the blank 28 which in the shapingof a blade It] assumes parti-cylindroidal configuration is denoted byreference numeral 52. The portion 52 is curved sharply forwardly so asto be tangent to the flat central portion 26 along a juncture line A-D.Accordingly, the portion 52 is curved along arcuate lines perpendicularto the line AD. That portion of section line 44 to the left of line ADis representative of said arcuate, lines and Fig. 4 graphicallyillustrates the sharp arc of forward curvature of the portion 52. Theradius of curvature of the portion 52 is selected to approximately equalthe radius of curvature of the portion 50. However, slight variationsbetween the radii of curvature of the said portions will not materiallyaffect the operating characteristics of the fan.

The location of the lines of tangency or juncture lines AC and AD isimportant. As will be seen from the drawings, said lines are angularlyrelated and intersect at the point A on line AB, said point being on ornear the midpoint of the peripheral edge 32. Thus the juncture linesdiverge toward the hub of the fan or toward the inner arcuate edge 34 ofeach blade 10 to define the flat central portion 26 of each blade 10 asbeing generally triangular. The angle CAD is thus defined by thejuncture lines with the point C on the leading edge 36 and the point Don the trailing edge 42, the said points C and D being substantiallyspaced from the inner end or edge of the blank at 34. Angle CAD may varythroughout a range of approximately 70 to approximately 90. For example,in the 11 fan shown, an angle of approximately 82 is preferred. AngleCAB between juncture line A--C and line AB is preferably less than theangle BAD between line A--B and juncture line AD. In the specificexample shown, angle CAB is approximately 39 and angle BAD isapproximately 43.

When a formed blade 10 is connected to the fan as by the spider 18, theblades central portion 26 assumes the basic pitch angle of the spiderarms 22, 22. The curved leading and trailing portions 50 and 52 vary inpitch due to their curved configuration. The variations in pitch of theportions 50 and 52 are best illustrated by Figs. 5. 6 and 7. The arcuatelines '55, 66 and 7-7 (Fig. l) are struck from the axis of rotation ofthe fan so the pitch angles illustrated by Figs. 5, 6 and 7 closelyapproximate the true pitch angles or angles of bite of the blade whenthe same is rotated. It will be noted by comparing Figs. 5, 6 and 7 thatthe angle of pitch along the leading edge 36 increases fromapproximately at the intersection at 38 of the leading and peripheraledges to the basic pitch angle at point C where the leading junctureline AC intersects the leading edge 36. In Fig. the leading edge has apitch angle slightly greater than 0 because section 5-5 is spacedinwardly from the peripheral edge. In Fig. 7 the leading edge has apitch angle less than the basic pitch because section 7-7 is spacedoutwardly from point C.

It will also be noted that the angle of pitch along the trailing edge 42has a maximum at the intersection at 44 of the trailing edge 42 andperipheral edge 32 and decreases from the said maximum to the basicpitch angle at the point D where the trailing juncture line ADintersects the trailing edge 42. The said maximum pitch 4 angle ispreferably approximately twice the basic pitch angle, but it may beslightly less than twice the said basic pitch angle and is shown asbeing about 60.

It will be apparent from the foregoing that the pitch angles of theleading and trailing edges of each blade vary inversely of each otherdue to the sharply forwardly curved leading and trailing portions beingtangent to the fiat central portion along angularly related juncturelines which intersect at the peripheral edge of the blade. The radii ofcurvature of the said leading and trailing portions are selected aspointed out hereinbefore to provide a pitch angle of approximately 0 atthe intersection of the leading and peripheral edges and a pitch angleat the intersection of the trailing and peripheral edges which isapproximately twice the basic pitch angle. In many installations theradii of said portions will be equal. The selection of the radius forthe leading portion is critical, it being most desirable to provide a 0pitch angle on the leading edge at the peripheral edge. The selection ofthe radius for the trailing portion is less critical, because it isbelieved that slight departures will not seriously alter the performancecharacteristics of the fan.

It has been found that a fan utilizing the abovedescribed blades ischaracterized by its quiet operation and by other desirable features.

For example, in one installation wherein a fan must be operated at aparticular speed by a particular motor under prescribed constantconditions of air flow and wherein the operating noise level must bemaintained below a maximum decibel rating, the fan of the presentinvention was found to be particularly well suited as compared toconventional fans known to us. It was found that conventional fans whichsuited the space requirements and which were pitched to govern the motorspeed as desired, caused excessive air flow and operated at undesirablyhigh noise levels. Altering the pitch angle proved to be no solutionbecause a variety of operating speeds resulted and the air flow variedwhile the noise level remained high.

It is believed that the fan of present invention was successful in saidinstallation because of the sharply forwardly curved leading andtrailing portions arranged as described herein to inversely vary thepitch along the leading and trailing edges. It is thought that thecurved leading portion caused the reduction in the operational noiselevel and that the curved trailing portion increased the brakehorsepower of the fan to govern the operating speed under the prescribedair flow conditions.

While the theory of operation is not fully understood, it is believedthat the best results will be attained in fans of various sizes and forvarious uses if the fans are constructed in proportion to the embodimentshown. For example, in a 22 fan, with blades set at a basic pitch of 33,it would be desirable to have 3" radii of curvature for the curvedleading and trailing portions of the blades to compare with the 1 /2radii for the curved portions of the blades in the 11" fan shown anddescribed.

The invention claimed is:

l. A fan rotatable about a central axis and comprising a plurality ofsimilar circumaxially spaced blades each of which is a single metallicsheet having a width greater than its radial dimension and having anarcuate peripheral edge and an inner end and consisting in part of aflat central portion and consisting further of leading and trailingportions joining the said central portion, the said central portionbeing located at a fixed basic pitch angle with respect to a planeperpendicular to the said axis and being bounded in part by inwardlydiverging lead ing and trailing juncture lines at opposite sides of acentral radial line and intersecting the said peripheral edge near thesaid radial line which diverging juncture lines have the included anglebetween them within the range of 70 to the said leading portion havingan exposed convex leading edge uniformly curved throughout the majorportion of its length and the said leading portion being forwardlycurved to conform approximately to a section of a cylinder which has aradius within the range of from 18% to 36% of the fan radius and whichis tangent to the said fiat central portion along the said leadingjuncture line and which extends from the last said juncture line to thesaid exposed convex leading edge, and the said trailing portion havingan exposed convex trailing edge uniformly curved throughout the majorportion of its length and the said trailing portion being forwardlycurved to conform approximately to a section of a cylinder which has aradius within the range of from 18% to 36% of the fan radius and whichis tangent to the said flat central portion along the said trailingjuncture line and which extends from the last said juncture line to thesaid exposed convex trailing edge.

2. A fan as set forth in claim 1, wherein the radius of the leadingcylindrical section of the blade is such that the pitch angle of thesaid leading edge is approximately Zero at a point immediately adjacentthe peripheral edge of the blade and increases inwardly along the saidleading edge to the said basic pitch angle at the intersection of theleading juncture line with the said leading edge, and wherein the radiusof the trailing cylindrical section of the blade is such that the pitchangle of the trailing edge is approximately twice the basic pitch angleat a point immediately adjacent the peripheral edge of the blade anddecreases inwardly along the said trailing edge to the said basic pitchangle at the intersection of the trailing juncture line with the saidtrailing edge.

3. A fan rotatable about a central axis and comprising a plurality ofsimilar circumaxially spaced blades each of which is a single metallicsheet having a width greater than its radial dimension and formed withan arcuate peripheral edge concentric with the axis and formed with anarcuate inner edge concentric with the axis and having a radius equal toabout 24% of the fan radius and the said sheet blade consisting furtherof leading and trailing portions joining the said central portion, thesaid central portion being located at a fixed basic pitch angle withrespect to a plane perpendicular to the said axis and being bounded inpart by leading and trailing juncture lines at opposite sides of acentral radial line and intersecting the said peripheral edge near thesaid radial line, which leading juncture line diverges inwardly from theradial line at an angle of about 39 and which trailing juncture linediverges inwardly from the radial line at an angle of about 43, the saidleading portion having an exposed leading edge which throughout themajor portion of its length conforms to an are having a radius equal toabout 45% of the fan radius and the said leading portion being forwardlycurved to conform approximately to a section of a cylinder which has aradius within the range of from 18% to 36% of the fan radius and whichis tangent to the said flat central portion along the said leadingjuncture line and which extends from the last said juncture line to thesaid exposed leading edge, and the said trailing portion having anexposed trailing edge which throughout the major portion of its lengthconforms to an arc having a radius equal to about 51% of the fan radiusand the said trailing portion being forwardly curved to conformapproximately to a section of a cylinder which has a radius within therange of from 18% to 36% of the fan radius and which is tangent to thesaid flat central portion along the said trailing juncture line andwhich extends from the last said juncture line to the said exposedtrailing edge.

References Cited in the file of this patent UNITED STATES PATENTS 41,706,608 Holmes Mar. 26, 1929 1,995,193 Stilphen Mar. 19, 19352,023,111 Alsing Dec. 3, 1935 2,031,466 Criqui Feb. 18, 1936 2,072,322Upson Mar. 2, 1937 2,581,873 Morrison Jan. 8, 1952

